CD200 is a transmembrane surface protein broadly expressed on a variety of cell types and delivers immunoregulatory signals through binding to receptor (CD200R) expressed on monocytes/myeloid cells and T lymphocytes. Stimulation of CD200R triggers an immune suppression response that is of interest medically in the treatment of autoimmune disorders including rheumatoid arthritis, lupus, asthma and in graft rejection and fetal loss.
Inhibition of the CD200: CD200R cascade inhibits CD200-mediated immune suppression, and thus augments the immune response. Agents that disrupt this interaction accordingly are of interest for the treatment of infectious diseases and cancers, and particularly hematopoietic cancers including leukemia, multiple myeloma and lymphoma as well as melanoma and other cancers (Moreaux et al. Biochem. Biophys. Res. Commun., 2008, 366:117-22). It has been suggested that certain AML tumour cells display an upregulated level of membrane-bound CD200, which can be diagnostic for tumours of this type. Various groups have also reported cellular CD200 overexpression associated with CLL, multiple myeloma, and melanoma (Petermann et al, J. Clin. Invest., 2007, 117(12):3922).
As a membrane-bound protein, cellular CD200 can be detected using cell or tissue-based assays, such as flow cytometry or immunohistochemical staining methods. The use of these techniques to detect cell surface CD200 overexpression in subjects presenting with CLL has been suggested, for instance, in US2005/0129690 to Bowdish et al published Jun. 16, 2005. However, it would be desirable to provide methods that are simple in their format, to facilitate detection of CD200, particularly in subjects afflicted with tumours and other medical conditions in which CD200 is overexpressed relative to healthy subjects.